What is the functional unit of contraction in a myofibril?

The striated appearance of myofibrils is due to the distribution pattern of two important proteins - Actin and Myosin. The light bands contain actin and the dark bands contain myosin.The light bands in a myofibril contain actin and is called I-band or Isotropic bandThe actin filaments are thinner as compared to the myosin filaments. Hence, they are commonly referred to as thin filaments and thick filaments, respectively.The portion of the myofibril between two successive "Z" lines is considered as the functional unit of contraction and is called a sarcomere.